My microfluidic pattern is made of SU-8 on the Si substrate. I tried to seal the pattern with a piece of PDMS. The PDMS is Oxygen plasma treated at 20W for 20s to achieve a hydrophlic surface toward the pattern. and SU-8 pattern also oxygen plasma treated under 100W for 1 minute after its hardbake at 150C. After that, two sides was contact and hot press at 100C for 2 hours in a vaccum oven. However, the bonding did not succeed. The problem probably comes from that the PDMS did not show the adhesive property to SU-8 once they were contacted. Actually, the PDMS is always show a "stick on" effect when it is contacted to other materials, such as glass dish, or Si substrate, even after the oxygen plasma treatment. But when it contact to my SU-8 pattern surface, the effect did not show up. I read a lot of work doing SU-8 and PDMS bonding with Oxygen treatment, but why does my work turns out that the PDMS seems does not have the possibility to be bonded on it?